The present invention relates to flexible liners for septic tanks, especially in a retrofit application. It is an object of the present invention to provide apparatus designed to facilitate the production of hollow cast articles such as septic tanks and concrete vaults, to facilitate separation between a carting and the forms used in making the casting, and to expedite the entire casting operation.
The prior art is filled with references to flexible tank liners and adaptations to fill and drain conduits, as well as upper and side support devices for the sidewalls. One example of a drain tank liner is shown in U.S. Pat. No. 5,656,766. A flexible liner forms a gas tight seal about the walls of an underground concrete vault. A concrete lid pressing on a circumferential flap at the top rectangular edge of the flexible liner provides support for the liner, such that the liner does not "slump" into the concrete vault and allow liquid to fill a space between the inner concrete wall and to outer surface of the flexible liner. It is especially important to note that the art in this patent recognizes that some adaptation is important for existing inlet pipes entering the concrete vault at a sidewall. A gasketed set of bolted plates seals the transition of a pipe entering the concrete vessel and passing into the flexible liner. The relatively heavy construction is the result of the impermissibility of leakage from the inside of the liner into the space between the liner and the concrete wall. U.S. Pat. No.5,656,766 thus illustrates several advantages and problems of flexible tank liners. Support and sidewall inlet pipe transitions are shown adapted to the special application of that patent, i.e., drainage pits primarily for the petroleum industry. An adaptation combining support and pipe/liner transition is seen in U.S. Pat. No. 4,653,663, wherein a rigid plate supporting the outside surface of the flexible is combined in opposition with an elastomeric plate on the inside surface of that liner.
Although not used to line storage tanks, the flexible liner of U.S. Pat. No. 4,388,357 shows that strips of liner stock can be fabricated on site to form a protective barrier against soil Regular Patent Application contamination by spilled oil, such as occurs at railroad tank car accidents in remote areas. The bottom of the fabricated flexible liner comprises a fabric screened drain so that the oil can be recovered for commercial use when the oil is withdrawn from the flexible liner. It would be especially useful to adapt flexible tank liner devices so that they could be used in situ, whereby none or relatively little of liquid in an existing storage tank would need to be removed. This is generally not practical in the art of lining tanks with flexible liners, i.e., the liquid is usually leaking into the environment outside of the tank or is further corroding the tank and destroying the support provided by the rigid tank walls.
U.S. Pat. No. 2,807,071 describes, and such description is incorporated herein, a casting apparatus comprising an inner form, a cover plate resting upon the inner form with respect to which file upper edges of the inner form are slidable, and means secured to the cover plate providing for limited upward movement thereof to facilitate separation between the cover plate and a completed-casting, with special application to casket vaults and extendible vaults, such extension being provided by stacking of a second or higher section above the base device described in that patent. The stacked piece is adapted to securingly mate with the piece beneath it, i.e., the cast article of U.S. Pat. No. 2,807,071 when formed comprises an upper inset rim which will accommodate a stacked section above it.
U.S. Pat. No. 3,990,673 describes the apparatus and method for casting concrete septic tanks, burial vaults and the like including an inner form and an outer form. The formation of concrete septic tanks burial vaults and other such structures generally contemplates the casting thereof in a "form". The form usually comprises an inner form and an outer form spaced apart from the inner form and into which the casting material, e.g. concrete, is poured. The outer form is usually a disassembleable rigid structure. The inner form comprises a rigid or expandable and collapsible side walls and end walls. The inner form also includes a top wall or cover plate which mates with the edges of the walls. The method of forming the cast article is basically providing a hollow inner form over which to pour concrete while also providing an outer form to force the concrete to be maintained against the inner form until the concrete hardens and the forms can be removed. The construction of concrete burial vaults is a very time consuming and labor intensive operation. The operation generally consisting of first constructing an inner form having a side wall and bottom wall configuration identical to the interior surfaces of the side wall and bottom wall of the vault to be formed. The inner form is then mounted a pallet or other flat base surface with the bottom wall of the inner form positioned for upwardly. An outer form consisting of four side walls having a configuration identical to the outer side wall configuration of a vault to be formed was assembled, i.e., typically pivotally hinged at a lower edge of the outer form, around the inner form. The form surfaces in contact with the concrete are next oiled. It is next conventional to suspend a wire mesh, "rebar" (reinforcing steel rods) or the like into the cavity formed by the inner form and the outer form to provide additional strength to concrete poured into the cavity. The form cavity is next filled with concrete and vibrated to remove voids and to fill the lower sections of the form cavity.